[Studies on fluorescent properties of multi-walled carbon nanotubes before and after concentrated nitric acid treatment]

Fluorescent properties of multi-walled carbon nanotubes (MWNTs) before and after concentrated nitric acid treatment were studied. The results show that both multi-walled carbon nanotubes (MWNTs) and treated multi-walled carbon nanotubes (t-MWNTs) could emit fluorescence; compared with MWNTs, fluorescence from t-MWNTs is stronger and fluorescent emission peak from t-MWNTs blue shifts slightly to short-wavelength. Luminescence from MWNTs could be related to the trapping of excitation energy at defect sites and the energy bandgap between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). Treating MWNTs with concentrated nitric acid could introduce more defects on MWNTs and make MWTNs trap more excitation energy, leading to a fluorescence enhancement of t-MWTNs; in addition, the energy bandgap between LUMO and HOMO increases with length decreasing of MWNT, and the shortening of MWNT caused by concentrated nitric acid treatment could make energy bandgap between LUMO and HOMO increase, resulting in a slight blue shift of fluorescent emission peak of t-MWTNs to short wavelength.